The invention relates to an apparatus for the three-dimensional inspection of hollow bodies;
having a conveyor for moving the hollow bodies through an inspection region over a circular path with simultaneous rotation of the hollow bodies about an axis of symmetry which is parallel to the axis of the circular path,
having an illuminating device for the hollow bodies which are in the inspection region,
having a photoelectric-detector to receive the light which issues from the hollow bodies which are in the inspection region, and
having a group of fixed, plane mirrors which are arranged in the path of light and at an angle to one another.
A apparatus of the above-mentioned kind known from EP-B1-0 151 059 serves for the inspection of the whole surface of translucent hollow bodies. The known apparatus has a continuously moved conveying star wheel as a conveyor, with which there is associated an external member for rotating the hollow bodies about their axis of symmetry. The illuminating device consists of a laser light source which directs a laser beam via a rotating mirror with a horizontal axis onto a group of four fixed, plane mirrors which are arranged one above the other in a vertical row. Because of the rotation of the rotating mirror, the plane mirrors deliver a vibrating beam of light which is thrown onto the hollow bodies via a vibrating mirror. The vibrating mirror accompanies the hollow bodies rotating in front of it, by its vibrating movement during a complete revolution and in the course of this sweeps over the hollow bodies with the beam of light in successive diametral planes. The photodetector is a receiver with a light-sensitive screen which is illuminated by the light shining through. In the known apparatus, a driving belt serves as a member for rotating the articles, which belt rests on the side of the hollow bodies adjacent to the light-sensitive screen, at their side wall, at an intermediate height and shades the hollow bodies in this region as a result. In order that this region situated in the blind angle may also be able to be inspected, the vertical row of fixed mirrors is provided, which deliver converging beams of light at different angles of inclination so that the whole surface of the hollow body can be inspected in the light shining through, circumventing the driving belt.
It is a disadvantage in the known apparatus that it needs moving mirrors, namely one rotating mirror and one vibrating mirror, the movement of which must be adapted precisely to one another and to the movement of the star wheel and must remain so adapted. This becomes particularly difficult if a line scanning camera or the like is used as a photodetector, the processor of which has to combine the individual lines at the right time to form a complete picture of the hollow body to be inspected. What is also problematical is that a moving mirror such as the vibrating mirror, which, in the known apparatus, is entrained by a mechanical cam in the direction of movement of the conveyor over the inspection region and is then rapidly returned, is subject to wear and at least require constant re-adjustment. In the known apparatus, however, the vibrating mirror cannot be dispensed with because otherwise no adequate inspection time would be available. There is no information in EP-B1-0 151 059 about the method of evaluating the pictures delivered by the light-sensitive screen of the known apparatus.
An apparatus which is provided for the inspection of the side walls of bottle is known from EP-A2-0 293 510. In this known apparatus, use is likewise made of a vibrating mirror and even of a vibrating lens in order to follow the bottle to be inspected from the beginning to the end of the inspection region. This known apparatus therefore has the same disadvantages as the known apparatus first mentioned above. In addition to this, the problems must be even greater when using a vibrating lens instead of a vibrating mirror, because the optical system must be moved extremely accurately if usable pictures are to be achieved at all.